This application generally relates measuring forces on a body, and in particular, an accelerometer used to measure forces in a stabilized platform system.
The Raytheon Company M-65 Airborne Tube-launched Optically-tracked Wire-to-command-link (“TOW”) system and the Kollsman Inc. Night Targeting System (similar to the M-65 system) use a pair of accelerometers to sense aircraft movement and assist the operator in tracking targets. These stabilized platform systems may be incorporated in vehicles and aircraft, such as the AH-1W USMC or other AH-I1 Cobra Attack Helicopter. It is estimated that there are at least 400 of these systems (or variants thereof) in use worldwide.
The TOW airborne system uses an accelerometer for each axis of its stabilized sight to sense aircraft movement with respect to the line of sight. This is used to correct the line-of-sight position for aircraft motion in order to maximize the probability of hit of the system. The conventional accelerometer module used in these system may utilize to Honeywell International Inc. Part No. 258970 (or equivalent), which interfaces with a mount to become an accelerometer module (e.g., Raytheon Part Nos. 3439031 or 3439030), or equivalents thereof. Two accelerometer modules may be provided, one for measuring acceleration in each of the elevation and azimuth directions.
Conventionally, the accelerometer modules outputs are integrated using electronics and this output is used to move the operator's line-of-sight to maintain the crosshair on a missile target, by correcting or compensating for the movement of the aircraft. The accelerometer modules are connected a 20 VAC, 900 Hz signal and provide a phase referenced AC signal for the motion compensating system. A similar system is disclosed, for example, in U.S. Pat. No. 3,829,659, incorporated herein by reference in its entirety.
FIG. 1 shows a block diagram of conventional accelerometer module 100 used for measuring acceleration in a stabilized platform system. Reference signal 110 is input to mechanical accelerometer 130. Typically, reference signal 110 is a 20 VAC, 900 Hz signal. In response to acceleration 50 applied to accelerator 130, accelerometer 130 generates an amplitude-modulated signal 160 which is provided to the avionics of the stabilized platform system for further processing.
Problems with conventional accelerometer modules 100 are that they are constructed using a mechanical strain gauge type accelerometer 130, which are very fragile and easily damaged due to severe shock and procuring original equipment manufacturer (OEM) replacement accelerometers may be very difficult and costly, particularly for systems with relatively long service lives.